1) Field of the Invention
The present invention relates to a power generation control apparatus for use in a motor vehicle, designed to control an output voltage of a generator for the vehicle by controlling its exciting current.
2) Description of the Related Art
A generator for use in a motor vehicle is for the purpose of charging a battery for replenishment while the vehicle is in a running condition and of providing electric power to various types of electrical equipment including ignition in an engine, illumination, and others, and a power generation control apparatus is connected thereto for maintaining an approximately constant output voltage even if the state of each of the electrical loads (current consumers) varies. In particular, recently, there is a tendency that the power generation torque of the vehicle generator increases with an increase in electrical load. When the power generation torque of the vehicle generator reaches an excessive value at the connection to an electrical load(s), the rotational operation of the engine becomes unstable, and for this reason, there has been known a technique to avoid such a situation through the implementation of gradually exciting control in which a power generation control apparatus increase an exciting current step by step.
For example, Japanese Patent Laid-Open No. SHO 62-064299 discloses a technique to suppress a rapid increase of the power generation torque by gradually increasing an exciting current for a vehicle generator, thereby preventing a reduction of the engine speed stemming from the rapid increase of the power generation torque of the vehicle generator when an electrical load is put into operation in an idling condition.
Meanwhile, in the recent years, there has been a tendency to lower the torque through the employment of various types of computerized auxiliary devices for the improvement of fuel consumption, while there has been an increasing requirement for higher output of the vehicle generator, and the movements of the power generation have exerted great influence on the variation of the engine revolution in an idling condition. For this reason, there arises a problem, however, in that the employment of only the method of varying the exciting current gradually through the use of the conventional technique disclosed in the above-mentioned publication cannot sufficiently prevent the engine revolution from being unstable. For example, in a case in which the engine revolutions lower rapidly due to some disturbance, the drive torque generated from the engine drops, while the power generation state of the vehicle generator having no load fluctuation is maintainable and the power generation torque increases, thus developing a reduction of the engine revolution and producing unstable engine revolution.